This project is concerned with the effects of reward sequence on rats' rate of learning to reverse a discrimination. The discrimination problem to be employed here is called successive brightness differential conditioning. In this task, two runways that differ in brightness will be presented on separate trials. Responses in one runway will be favorably rewarded; responses in the opposite runway will receive nonreward. Differential running speeds in the two runways will provide a measure of discrimination. This task was chosen because of the high degree of control it allows over presentation sequence of the discriminanda and because it was this task that initially provided evidence of sequential effects in discrimination learning. Sequential effects in differential conditioning have been attributed to the behavioral control acquired by internal reward-produced cues even though brightness cues were relevant to solving the problem. The proposed experiments would provide additional information about how internal cues acquire control over discriminative behavior. Understanding internal stimulus control in discrimination learning is particularly important for two reasons. Differential reward-produced cues are an inherent feature of discrimination learning; and, reward-produced cues may well be intrinsically more significant to the rat than external cues conventionally employed as discriminanda.